Heteropogon ‐ Themeda grasses evolve to occupy either tropical grassland or wetland biomes

Species of the Heteropogon‐Themeda clade are ecologically important grasses distributed across the tropics, including widespread species, such as the pantropical Heteropogon contortus and Themeda triandra, and range‐restricted species such as Heteropogon ritchiei and Themeda anathera. Here, we examine habitat preferences of the grassland/savanna and wetland species by describing bioclimatic niche characteristics, characterizing functional traits, and investigating the evolution of functional traits of 31 species in the Heteropogon‐Themeda clade in relation to precipitation and temperature. The climatic limits of the clade are linked to mean annual precipitation and seasonality that also distinguish seven wetland species from 24 grassland/savanna species. Tests of niche equivalency highlighted the unique bioclimatic niche of the wetland species. However, climatic factors do not fully explain species geographic range, and other factors are likely to contribute to their distribution ranges. Trait analyses demonstrated that the wetland and grassland/savanna species were separated by culm height, leaf length, leaf area, awn length, and awn types. Phylogenetic analyses showed that the wetland species had tall stature with long and large leaves and lack of hygroscopic awns, which suggest selective pressures in the shift between savanna/grassland and wetland. The two most widespread species, H. contortus and T. triandra, have significantly different bioclimatic niches, but we also found that climatic niche alone does not explain the current geographic distributions of H. contortus and T. triandra. Our study provides a new understanding of the biogeography and evolutionary history of an ecologically important clade of C4 tropical grasses

Taxonomy, evolutionary history, and ecological dominance of Themeda and Heteropogon.

Heteropogon and Themeda grasses are common and significant components of the C4 savannas which have recently gained more attention for conservation and biodiversity research. The two genera have been the subject of ecological research due to their widespread and dominant species H. contortus and T. themeda. Like many tropical plant lineages, however, in-depth knowledge necessary for the management of these ecosystems is still lacking. This thesis focuses on the diversity of Heteropogon and Themeda in respect to evolution, ecology, and systematics. In this thesis, phylogenetic analyses indicated that the evolutionary history of Heteropogon and Themeda is being driven by complex evolutionary processes and their origin is dated back to the Miocene grassland expansion. I interpreted those discordant phylogenetic placements between plastid and nuclear trees as underlying polyploidization or hybridization within the groups. Dating analyses indicated that most species originated in the Miocene grassland expansion. Widespread species, H. contortus and T. triandra did not originate until the Late Miocene and quickly spread throughout the Tropics in the Pleistocene. Climatic niche characteristics and geographic distributions of Heteropogon and Themeda shed light on macroecological patterns, adaptation by functional traits, and the evolution of climatic niche and functional traits. I found that Heteropogon and Themeda species are separated into savanna and wetland groups. This is supported by differences in precipitation regimes of the two habitats and functional traits (e.g., plant height, leaf area, and awns). In an evolutionary context, biomes were shifted from savannas to wetlands, and niche divergence occurred. Functional traits changed by habitat preferences and show lability in the lineage. Integration of morphology and new ecological and phylogenetic evidence derived from this thesis were used in new generic and species reclassifications of Heteropogon and Themeda. I conclude that the generic description of Heteropogon should be narrowed, and I accept three species, while that of Themeda expanded to accept 26 Themeda species and 2 varieties. Phylogenetic relationships determine diagnostic morphological characters in generic and species delimitations. This new systematics of Heteropogon and Themeda demonstrates how to apply various biological data in taxonomic revision, and to summarize biodiversity information of Heteropogon and Themeda

Taxonomy, evolutionary history, and ecological dominance of Themeda and Heteropogon

Heteropogon and Themeda grasses are common and significant components of the C4 savannas which have recently gained more attention for conservation and biodiversity research. The two genera have been the subject of ecological research due to their widespread and dominant species H. contortus and T. themeda. Like many tropical plant lineages, however, in-depth knowledge necessary for the management of these ecosystems is still lacking. This thesis focuses on the diversity of Heteropogon and Themeda in respect to evolution, ecology, and systematics. In this thesis, phylogenetic analyses indicated that the evolutionary history of Heteropogon and Themeda is being driven by complex evolutionary processes and their origin is dated back to the Miocene grassland expansion. I interpreted those discordant phylogenetic placements between plastid and nuclear trees as underlying polyploidization or hybridization within the groups. Dating analyses indicated that most species originated in the Miocene grassland expansion. Widespread species, H. contortus and T. triandra did not originate until the Late Miocene and quickly spread throughout the Tropics in the Pleistocene. Climatic niche characteristics and geographic distributions of Heteropogon and Themeda shed light on macroecological patterns, adaptation by functional traits, and the evolution of climatic niche and functional traits. I found that Heteropogon and Themeda species are separated into savanna and wetland groups. This is supported by differences in precipitation regimes of the two habitats and functional traits (e.g., plant height, leaf area, and awns). In an evolutionary context, biomes were shifted from savannas to wetlands, and niche divergence occurred. Functional traits changed by habitat preferences and show lability in the lineage. Integration of morphology and new ecological and phylogenetic evidence derived from this thesis were used in new generic and species reclassifications of Heteropogon and Themeda. I conclude that the generic description of Heteropogon should be narrowed, and I accept three species, while that of Themeda expanded to accept 26 Themeda species and 2 varieties. Phylogenetic relationships determine diagnostic morphological characters in generic and species delimitations. This new systematics of Heteropogon and Themeda demonstrates how to apply various biological data in taxonomic revision, and to summarize biodiversity information of Heteropogon and Themeda

Data from: Phylogenomics of Andropogoneae (Panicoideae: Poaceae) of mainland Southeast Asia

The grass tribe Andropogoneae is distributed in warm regions around the globe but has been poorly studied in mainland Southeast Asia. This is particularly true for the cosmopolitan genera Andropogon and Schizachyrium, with several species that appear to be narrowly distributed in this region. Additionally, lesser-known species in the genera Hemisorghum, Kerriochloa, and Pseudosorghum also occur in mainland Southeast Asia. A phylogeny is needed to address questions of taxonomy and trait evolution. Whole chloroplast genomes of Andropogoneae species and two outgroup species of Garnotia (tribe Arundinelleae) were analyzed using maximum likelihood (ML) and Bayesian inference (BI). Ancestral character states were reconstructed using ML for four morphological characters key to Andropogon and Schizachyrium identification. A previously-unidentified clade of Southeast Asian endemic taxa is found, including one species formerly classified in Andropogon. Other Southeast Asian taxa fall in an unresolved grade outside the major radiation of the tribe. Andropogon and Schizachyrium are both polyphyletic. Convergent evolution and reversal of characters are common throughout Andropogoneae. Addition of species from mainland Southeast Asian finds unexpected phylogenetic diversity. Southeast Asian Schizachyrium sanguineum forms two separate clades, which could reflect cryptic species differentiation, hybridization, introgression, or some combination

Phylogenomics and the rise of the angiosperms

International audienceAngiosperms are the cornerstone of most terrestrial ecosystems and human livelihoods 1,2 . A robust understanding of angiosperm evolution is required to explain their rise to ecological dominance. So far, the angiosperm tree of life has been determined primarily by means of analyses of the plastid genome 3,4 . Many studies have drawn on this foundational work, such as classification and first insights into angiosperm diversification since their Mesozoic origins 5–7 . However, the limited and biased sampling of both taxa and genomes undermines confidence in the tree and its implications. Here, we build the tree of life for almost 8,000 (about 60%) angiosperm genera using a standardized set of 353 nuclear genes 8 . This 15-fold increase in genus-level sampling relative to comparable nuclear studies 9 provides a critical test of earlier results and brings notable change to key groups, especially in rosids, while substantiating many previously predicted relationships. Scaling this tree to time using 200 fossils, we discovered that early angiosperm evolution was characterized by high gene tree conflict and explosive diversification, giving rise to more than 80% of extant angiosperm orders. Steady diversification ensued through the remaining Mesozoic Era until rates resurged in the Cenozoic Era, concurrent with decreasing global temperatures and tightly linked with gene tree conflict. Taken together, our extensive sampling combined with advanced phylogenomic methods shows the deep history and full complexity in the evolution of a megadiverse clade

Phylogenomics and the rise of the angiosperms.

Angiosperms are the cornerstone of most terrestrial ecosystems and human livelihoods1,2. A robust understanding of angiosperm evolution is required to explain their rise to ecological dominance. So far, the angiosperm tree of life has been determined primarily by means of analyses of the plastid genome3,4. Many studies have drawn on this foundational work, such as classification and first insights into angiosperm diversification since their Mesozoic origins5-7. However, the limited and biased sampling of both taxa and genomes undermines confidence in the tree and its implications. Here, we build the tree of life for almost 8,000 (about 60%) angiosperm genera using a standardized set of 353 nuclear genes8. This 15-fold increase in genus-level sampling relative to comparable nuclear studies9 provides a critical test of earlier results and brings notable change to key groups, especially in rosids, while substantiating many previously predicted relationships. Scaling this tree to time using 200 fossils, we discovered that early angiosperm evolution was characterized by high gene tree conflict and explosive diversification, giving rise to more than 80% of extant angiosperm orders. Steady diversification ensued through the remaining Mesozoic Era until rates resurged in the Cenozoic Era, concurrent with decreasing global temperatures and tightly linked with gene tree conflict. Taken together, our extensive sampling combined with advanced phylogenomic methods shows the deep history and full complexity in the evolution of a megadiverse clade